How do I determine size of ANSI terminal?

Question

Standard input and output are connected to a terminal that implements ANSI escape sequences, but is of unknown dimensions.

I need to know how big the terminal so to

Answer 1

The resize program does this by moving the cursor to a very large column and row; the terminal moves as far as it can, e.g.,

CUP 999 999

Then resize asks where the cursor is:

DSR 6

The terminal replies with the actual cursor position (i.e., the cursor position report CPR), from which resize knows the terminal's size: the cursor is on the lower-right corner.

That's all done using standard (ECMA-48 / VT100) escape sequences. In XTerm Control Sequences (which should apply to your "ANSI" terminal)

CSI Ps n  Device Status Report (DSR).
            Ps = 6  -> Report Cursor Position (CPR) [row;column].
          Result is CSI r ; c R